There is a general need for readily regulatable promoters to control gene expression in a variety of experimental and commercial applications. Currently, the majority of such systems that have been developed are based on the administration of chemical effectors which require diffusion into the cell to provide appropriate, non-toxic concentrations of chemical at the target-gene site. This can be problematic, because of the potential for toxic, unintended or pleiotropic effects of the inducing chemical, and especially in multicellular organisms, where synchronous spatial and temporal induction or repression of target gene expression is desired in all cells. There is thus a tremendous need to develop an artificial promoter system that can be fused upstream of any desired gene enabling reversible induction or repression of the expression of the gene at will in any suitable host cell or organisms by light.